In many of today's most popular electronic devices, such as cell phones, laptop computers, personal data organizers, and global positioning systems, chip to chip communication is a required element of the architecture. Data may be transmitted across short distances between integrated circuits within the device.
The transmission of data involves sending and receiving data over a transmission path, which is connected between a pair of transceivers. Each transceiver can have a receiver and a transmitter (or driver). In this manner, the receiver functions to receive data from the transmission path, whereas the transmitter functions to drive data onto the transmission path. The transfer of data between receiver and transmitter circuits fabricated on separate chips is sometimes referred to as “off-chip” signaling or “chip to chip” communication.
Single-ended signals are typically used for on-chip communication because of the reduced area consumption and design complexity generally involved in routing these signals. However, more and more off-chip signals, or signals used for chip to chip communication, are routed as differential signals because of their decreased sensitivity to environmental noise. For this reason, numerous transmission protocols such as Low Voltage Differential Signals (LVDS), Stub Series Terminated Logic (SSTL), differential High-Speed Transceiver Logic (HSTL) and Low Voltage Positive Referenced Emitter Coupled Logic (LVPECL) have been established for sending and receiving differential signals across a transmission path. These differential signals often have smaller amplitudes (i.e., reduced swings) to facilitate easier routing in high speed chip-to-chip communications. In addition, the common mode voltage (i.e., the average voltage value) of the differential signals often varies significantly from case to case depending on the actual application environment.
A differential receiver essentially operates as a differential sense amplifier that can ideally accept a relatively wide input common mode voltage range with a high common mode rejection ratio. However, as with most circuits, a practical sense amplifier has a limit as to the common mode voltage that it can accept. One of the difficulties in sensing the differential signal is the asymmetrical switching of the output lines due to process and switching speed variations in the transmitter. Process yield can be adversely impacted by a process corner that produces a characteristically fast p-channel Metal Oxide Semiconductor (pMOS) transistor coupled to a characteristically slow n-channel Metal Oxide Semiconductor (nMOS) transistor or vice versa.
The difficulty arises when the differential signals reach an equal voltage level that is distant and different from the reference voltage. This condition may produce shifted timing of the input data of the receiver, which may cause data corruption. Since the performance of the chip to chip communication may be impacted by temperature and voltage variations as well, maintaining tight process control is critical. Unfortunately normal statistical distribution occurs despite the efforts to produce only nominal speed devices. The current state of the art may render the devices, which are produced and fall outside of the nominal speed range, non-operational across their specified temperature and voltage ranges.
Thus, a need still remains for an integrated circuit communication system with differential signal that can increase the manufacturing yield of the chip to chip communication to include product that is fabricated outside the nominal process. In view of the increased demand for highly integrated functions that require chip to chip communication, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.